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This image shows the strip of sky imaged during Planck's two week "First Light Survey" in August 2009. The background image shows the whole sky in visible light, with the plane of our Galaxy running across the middle. The coloured strip is Planck's view of the sky at a wavelength of 3mm (a frequency of 100 GHz), covering around 10% of the sky. Most of the strip is dominated by the Cosmic Microwave Background (CMB), but the Galaxy can be seen across the middle.

Hover the mouse over to compare a patch of sky as seen by Planck two instruments, showing only very subtle variations between the two. You can also download the individual 70 GHz and 100 GHz images. Image credit: ESA / LFI / HFI

The first light survey has proven that both of Planck's instruments are working very well. The small box near the top of the image shows a region where the CMB can be seen clearly, and this should look very similar to both of Planck's instruments. The image on the right shows that patch as seen by the Low Frequency Instrument at 70 GHz and the HFI instrument at 100 GHz. The hot (red) and cold (blue) patches match very well, with any subtle differences being due to tenuous emission from our Galaxy.

One of Planck's major advantages of other experiments is its broad frequency coverage, with 9 bands covering frequencies of 30 GHz up to 850 GHz, corresponding to wavelengths of 1cm down to 0.3 mm. This provides a factor of nearly 30 between the lowest and highest frequencies, and allows Planck do distinguish between the CMB and emisison from our own Galaxy far better than has been possible before. The image below shows a small patch of sky looking through the plane of our Galaxy, at all nine of Planck's frequency channels.

A patch of sky showing the Galactic plane at all nine of Planck's frequencies. At low frequencies, gas and electrons dominate, in the middle the CMB shos through faintly, while at high frequencies cold dust is seen. Image credits: ESA / LFI / HFI.